Which is true about disruptive selection?
A) The fitness curve is higher in the middle than at either end.
B) The fitness curve is higher on one end.
C) The fitness curve is higher on both ends than in the middle.
D) The fitness curve changes over time.
The correct answer and explanation is:
The correct answer is C) The fitness curve is higher on both ends than in the middle.
Disruptive selection is a type of natural selection where extreme values of a trait are favored over intermediate values. In this case, individuals with traits at either end of a spectrum (for example, very small or very large) have higher fitness compared to those with average traits. As a result, the population may eventually split into two distinct groups, each with extreme traits, while the intermediate group may decline or even disappear.
To visualize this, imagine a fitness curve that shows how well individuals of different trait values (such as size, color, or shape) survive and reproduce. In disruptive selection, the curve is bimodal, meaning it has two peaks: one at each extreme of the trait spectrum. The middle of the curve, representing average traits, has a low fitness value.
This selection pattern typically occurs in environments where resources or niches are divided, and organisms with extreme traits are better suited to exploit those resources. For instance, in an environment where both small and large beaks are advantageous for feeding on different types of seeds, birds with medium-sized beaks may be less efficient at accessing both types of seeds, leading to the decline of medium-sized beaked birds.
Disruptive selection can ultimately drive speciation, as populations with distinct extremes of a trait may evolve into separate species over time. It is the opposite of stabilizing selection, which favors intermediate traits, and directional selection, which favors one extreme.